Grant McCann, Josh Wright and Martyn Woolford were the only players not to play a full ninety minutes, giving way to O'Connor, Morris and Togwell in the second half.
United dominated much of a fiesty affair at Blundell Park, a game that looked as though it was going to boil over at times in the first half. Byrne, McCann and Hooper were all involved in scuffles early on however referee Shaun Proctor Green decided against taking further action and kept his cards in his pocket until the second half.
They took a deserved lead after 20 minutes when Byrne headed across the face of the goal and Hooper turned the ball home at the near post.
Rob Jones, who looked a little shaky on his return to Blundell Park also had one cleared off the line before Hayes made it two. A searching ball from McCann was headed into his path by Hooper, and Hayes' curling effort bounced over the Grimsby keeper.
In the second half United looked bright sealed the victory with a well executed free kick. O'Connor, who's range of passing was impressive, clipped in a delightful ball to Hayes, who turned and poked home for his second of the night.
Adam Proudlock picked up a booking for Grimsby after a series of verbals towards the referee.
It could have been more in the closing stages, Hooper blasted over before laying the ball across to Togwell after a mazy run on the right wing, however the former Barnsley midfielder blazed over the empty net.
Hooper could have added a fourth and doubled his tally in the last minute, but headed against the post from three yards.